1. Field of the Invention.
The present invention relates to missile airframes and, more particularly, to means for expanding a missile airframe after launch to provide additional clearance in front of a shaped charge warhead used against armored targets.
2. Description of the Related Art.
The use of shaped explosive charges has become widespread in modern ordnance. Present technology typically utilizes a conical charge in contact with a conical metal liner. When the charge is detonated, the liner is converted by the resulting shockwave into a penetrating jet of metal plasma coincident with the axis of the undetonated charge. Such shaped charges have been utilized in projectiles designed to penetrate heavy armor and fortifications such as bunkers.
In the face of the shaped-charge threat, reactive armor has been developed which incorporates small explosive charges in the armor's outer layer. The function of such small explosive charges is to disrupt the shockwave formed by a shaped charge.
With the advent of reactive armor, tandem warheads have been developed. A tandem warhead utilizes twin shaped charges--a minor charge for triggering the reactive armor and a main charge for penetrating the armor once the reactive function has been disabled.
The efficacy of the shaped charge is highly dependent on the warhead-to-target distance at the time of main charge detonation, as time is required for the jet of metal plasma to fully form. Maximum armor penetration will generally occur when this distance is approximately six times the diameter of the main charge, although a "standoff" distance of about two diameters will still produce a satisfactory result. Since the main charge cannot be detonated until the minor charge has disabled the reactive function of the armor, the standoff distance at the time of main charge detonation cannot be greater than the distance separating the minor and main charges.
At present, the design of missile airframes allows for only a fixed separation between the two charges of a tandem warhead. Such separation is likely to be less than optimum. It would be a great advance in the art of military ordnance to create a missile airframe which could provide the optimum "standoff" distance without sacrificing the ease of storage and handling that accompanies the shorter lengths associated with present designs. A missile airframe which could be transformed after launch from a short initial configuration to a longer configuration with increased standoff would facilitate storage, handling and transport. The increased standoff resulting from the longer configuration would increase target penetration ability.
Some examples of schemes for lengthening projectiles in flight are summarized below.
U.S. Pat. No. 46,490 to Orwig is directed to a projectile with a telescoping stem provided with wings in such a manner that the stem is contracted within the limits of the cartridge bag before firing, but as soon as the projectile leaves the muzzle of the barrel the stem elongates by its own inertia and atmospheric resistance to give balance and steadiness to the projectile in its flight. The stem is secured to a cap which is perforated with holes through which the cartridge bag is filled with powder before attachment to the projectile.
U.S. Pat. No. 1,049,144 to Quisling relates to projectiles which are steered without rotation by means of a rearward extension of the projectile. The steering member is constructed as a sleeve enclosing the projectile and being closed at the rear end by a cap. While in the barrel, the projectile is forced forward in the sleeve by the pressure of the gas generated in the projectile, pressing against the interior of the cap while the latter is forced forward by the driving charge. The gas escapes automatically as soon as its pressure exceeds by a certain amount the pressure from the driving charge acting on the bottom of the cap sleeve, or after the projectile has moved forwardly a certain distance in the sleeve.
U.S. Pat. No. 2,344,957 to Anzalone is directed to a pistol-fired rocket flare equipped with a guiding device comprising a cylindrical sleeve, slidable on the rocket casing, to which four radial vanes are attached at 90 degree intervals along the periphery of the sleeve. After the rocket flare is fired from the pistol, the vanes slide rearward on the casing.
U.S. Pat. No. 2,409,904 to Schermuly et al is directed to a rocket provided with a sliding tail. The rocket comprises a casing, one or more bands slidable on the casing, tail elements secured to said bands and a stop on the casing to limit the rearward movement of the bands along the casing. Means may be provided for locking the tail in position when the bands have engaged the stop.
U.S. Pat. No. 2,426,239 to Renner is directed to a round of ammunition with a telescoping tail structure having a base which is reduced in diameter and provided with external threads while a cup-like cavity extends forward into the body of the projectile a sufficient distance to house an auxiliary propellant charge suitable for propelling a rocket. The auxiliary charge is ignited after the projectile assembly clears the gun muzzle a sufficient distance to extend tube and tail segments. Gas escaping through a fuse tube and rocket tubes exerts an additional propelling influence on the projectile assembly. Blast from the rocket tubes deflected by curved vane surfaces tends to stabilize the assembly by maintaining it in rotation, although the bulk of the stabilizing influence comes from the flow of air through the vanes.
U.S. Pat. No. 2,507,878 to Banning, Jr., is directed to a projectile for ordnance comprising a shot section having its base portion provided with a forwardly, outwardly and rearwardly curved surface facing towards the gases released from the gun in which the projectile is used. The gases released from the muzzle impinge against the curved surfaces of the projectile base and are deflected rearwardly with a consequent increase of muzzle energy of the projectile. A rearwardly extending skirt telescopingly mounted on the projectile has a size to cooperate with the bore of the gun and maintain substantially gastight engagement with the bore after passage of the curved surface past the muzzle and until departure of the skirt from the muzzle. The skirt has a series of gas discharge orifices therethrough substantially in the zone of the periphery of the rearwardly curved surface for discharge of gases during the interval between passage of the peripheral portion of the curved surface beyond the muzzle and the time or flight of the skirt portion from the muzzle.
U.S. Pat. No. 2,700,337 to Cumming is directed to a liquid propellant rocket provided with a movable injector, the movement of which enlarges the combustion chamber and also forces liquid propellant into the combustion chamber. Enlargement of the combustion chamber provides maximum combustion efficiency. Injection of the liquid propellant into the combustion chamber by the movable injector eliminates a separate pressurizing or pumping system.
U.S. Pat. No. 2,935,946 to Gallo et al is directed to a telescoping ram jet construction. A center body portion of the projectile is designed to be telescoped within the combustion chamber when the combustion chamber is not in use. The center body portion houses the fuse, warhead, and fuel tank as well as fuel metering valves and ignition means. Upon firing, the combustion shell is pushed to the rear by aerodynamic forces to expand the projectile to operating position.
U.S. Pat. No. 3,256,816 to Pilcher is directed to an extending boom for sounding rockets and, more particularly, to a device that displaces an instrument away from the main body of a rocket and then holds that instrument at the new position for the remainder of the rocket flight. The extending boom acts as an integral part of the payload structure of the rocket and is of sufficient strength to support the whole forward section of the payload structure in its extended position. The boom is further capable of being stowed in the rocket's nose cone. Air at atmospheric pressure inside the rocket is used to extend the boom.
U.S. Pat. No. 3,347,491 to Pickart is directed to a firearm projectile provided with a device for slowing down or braking. The device comprises at least one member displaceable due to its elasticity or plasticity or its mobility, towards the exterior of the periphery of the projectile or towards the rear of the projectile, or in both these directions to increase the surface of friction in the air. The device may comprise a plurality of small tongue members or an element sliding to the rear under the effect of a spring.
U.S. Pat. No. 3,698,320 to Cochran et al relates to a rocket with a body of cylindrical form and an ogive head over which a sleeve is slidably disposed in nested relation for storage. The sleeve slides rearwardly upon initial movement of the rocket so as to extend from the rear end thereof. The telescoping rear sleeve is used for stabilization of the rocket in flight.
None of the references described briefly above discloses a telescoping missile airframe which extends after launch to increase the separation between tandem shaped charges.